Gas insulated switchgear is configured so as to include a main bus, a circuit breaker, a disconnector/earth switch, a current transformer, and a pressure container in which high-pressure SF6 gas or the like is enclosed. Further, the main bus that is configured by using, for example, aluminum, copper, or the like is arranged so that a load current flows therethrough, while the main bus is disposed in the pressure container.
When the load current is caused to flow through the main bus, a magnetic field is generated in the surrounding thereof, so that the pressure container has eddy currents that flow in such a manner that the magnetic field is to be cancelled. For this reason, in the case where the material of which the pressure container is made, is a magnetic material, a problem related to Joule heating caused by the eddy currents arises. In this situation, in the case where the material of which the pressure container is made, is a magnetic material, because an induced current flows on the surface of the pressure container, the current density is large. In addition, because there is a large hysteresis loss, the increase in the temperature caused by the heat generation is also large. In contrast, in the case where the material of which the pressure container is made, is a non-magnetic material, because the induced current flows not only on the surface of the pressure container, but also with a certain depth, the current density is smaller. In addition, because the hysteresis loss is smaller, it is possible to inhibit the increase in the temperature caused by the heat generation. Further, generally speaking, the load current value to be used is different for each user, and the amount of heat generation of the pressure container is proportional to the square of the load current value. Thus, when the load current value increases, the amount of heat generation of the pressure container greatly changes. For example, although it is possible to use a pressure container made of a magnetic material when the load current value is 2000 amperes, the amount of heat generation corresponding to a load current value of 3000 amperes is approximately 2.3 times as large as the amount of heat generation corresponding to a load current value of 2000 amperes, so that, in some situations, it may be necessary to use a pressure container that is made of a non-magnetic material. In other words, in some situations, it is necessary to select between a pressure container made of a magnetic material and a pressure container made of a non-magnetic material, based on the load current value. Further, even if the load current value is at such a level that allows a pressure container made of a magnetic material to be used, if the exterior dimension of the pressure container is arranged to be small, the amount of heat generation increases, and it becomes necessary to use a pressure container that is made of a non-magnetic material. Because pressure containers have a high possibility of being touched by inspection staff during machine inspection processes or the like, it is obligated to inhibit the increase in the temperature of the pressure containers to the extent that no problem is caused even if someone touches the pressure containers.
Patent Document 1 describes a technique for inhibiting an increase in the temperature of a pressure container by providing an electrically-conductive member between a pair of nozzles disposed on the upper part of the pressure container so as to connect the pair of nozzles together, and causing eddy current to flow through the electrically-conductive member in a direction opposite to the flow of a load current.
Further, Patent Document 2 describes a configuration in which a pressure container is configured by using a clad plate that is obtained by joining a copper plate to the inside of a stainless steel plate. In this situation, because eddy current flows through the copper, which has lower resistivity, it is possible to inhibit an increase in the temperature of the pressure container without having to make the diameter of the pressure container large.    Patent Document 1: Japanese Patent Application Laid-open No. 2004-281302    Patent Document 2: Japanese Patent Application Laid-open No. H07-15814